<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  .wrap {
    background: #eee;
    overflow: hidden;
    /* < !-- 生成BFC，计算高度时考虑浮动的元素 -->padding: 20px; */
    height: 200px;
  }

  .left {
    width: 200px;
    height: 200px;
    float: left;
    background: coral;
  }

  .right {
    width: 120px;
    height: 200px;
    float: right;
    background: lightblue;
  }

  .middle {
    margin-left: 220px;
    height: 200px;
    background: lightpink;
    margin-right: 140px;
  }
</style>

<body>

  <div class="wrap">
    <div class="left">左侧</div>
    <div class="right">右侧</div>
    <div class="middle">中间</div>
  </div>
</body>

</html>